Three phase control system employing saturable reactors



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Patented Sept. 11, 1951 UNITED STATES PATENT OFFICE THREE PHASE CONTRDLSYSTEM EMPLOY- ING SATURABLE REACTOBS Raymond E. Morgan, Schenectady, N.Y., assignor to General Electric Company, a corporation o! New YorkApplication October 31, 1850, Serial No. 193,171

2 Claims. (Cl. 321-25) an economical magnetic ampliiier three phasecontrol circuit which employs saturable reactor means having fourreactance windings instead oi the usual six reactance windings.

A still further object of my invention is to provide a three phasemagnetic amplifier control system which does not require additionalcurrent commutating elements for inductive loads.

In general, my invention comprises saturable reactor means having twopair of reactance windings, each pair connected in circuit rela.- tionwith a direct current consumption circuit or load through tull'wavedouble-bridge current rectifying means in a manner such thatunidirectional current flows through the consumption circuit from twoo1' the requisite three input conductors through different reactancewindings to the third conductor during only four of the six alternationsof one complete cycle of three phase source voltage. Commutation forinductive loads is provided by a portion of the full wave currentrectiiying means connected between the load and the third inputconductor.

AThe novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, together with further objects and advantages thereofmay best be understood by reference to the following description takenin connection with the accompanying drawing in which Fig. 1 is adiagrammatic view of one embodiment of my novel control system and Fig.2 is a schematic diagram of the control system of Fig. i helpful in theexplanation of the operation thereof.

Referring to Fig. 1, I have shown my invention in one form as comprisinga. saturable rewith reactor Il while reactance windings Il, Il andcontrol winding It are associated with'reactor II. The control windingsI6 and Il' are connected in series between suitable control signal inputconductors I1 and I8 to provide a single control means ior controllingthe level of magnetic saturation in both core members simultaneouslyresponsive to the amplitude oi' a signal voltage supplied betweenconductors I1 and I2. Three alternating current supplying conductors I9,2l and 2|, one for each phase of a three phase alternating voltagesource, are connected through suitable full wave doublebridge currentrectifying means, such as by rectiiiers 22, 2l, 24, 2l, 26 and 21, tosuitable output terminals 2s and 30 across which a direct currentconsumption circuit, indicated as load 2l,

may be connected. Each pair of the reactance windings I2, I3, and Il, I5are connected in circuit relation with each of two input conductors I!and 2l respectively to provide four current paths through consumptioncircuit 28 to the third input conductor 2|. Rectiilers 22 through 21 arearranged with their directions of easy current iiow such that currentilows through the load 28 in only one direction from the conductors I!and 20 to the conductor 2| during each oi' four alternations of sourcecurrent supplied between these conductors during two -phases of thethree phase source voltage. In the preferred form of my inventionillustrated in the drawing. reactance windings I2 and I3 are eachconnected from conductor I9 through reversely lpoled rectiiiers 22 and24 to opposite sides of the load 28; reactance windings Il and I5 areeach similarly connected from conductor 2l through reversely poledrectiers 23, 25 across the load 28, while reversely poled rectiers 2Gand 21 are directly connected from conductor 2| across the load 28. Dueto 'the double-bridge type connection oi' these rectiflers, current canow in only one direction through the load 2l during the alternations ofany phase of the three phase alternating voltage source.

The operation of my magnetic ampliiier control system can best beunderstood by reference to Fig. 2 in which I have shown an equivalentcircuit diagram of the device shown in Fig. 1. In Fig. 2 I haverepresented the voltage between conductors I9 and 20 as phase I, thevoltage between conductors 20 and 2| as phase 2, and the voltage betweenconductors I9 and 2| as phase 3. Since only four reactance windings areemployed in this double-bridge rectifier connection, only two of thesethree phase signals,

assaggio namely, phase 2 and phase actually contribute to the currentthat hows through the load 28. Due to the prevalence of currents in thereactance windings i2 through i5 as aresult of the currents supplied byphase 2 and phase 3. any current which might flow through thesereactance windings and load 2S as a re sult of the phase i cycle, issuppressed. Consequently, only iour unidirectional pulses oi currentpass through the load 2t during one ruil cycle of three phasealternating voltage source, and the magnitude or these four pulses maybe controlled by the amplitude lof a control voltage supplied to thecontrol windings land I8 so as to vary the time of saturation of thereactors It and il associated with windings I2 through I5. Reactancewindings It through I are wound or connected in the circuit so as toproduce a magnetic iiux which is in the same direction in each of thesaturable reactors i@ and Il, as indicated by the arrows, so that achange in control winding iiux and consequent change in the saturationtime of the reactors occurs in the same direction in both reactors.

The specific paths of current for thephase 2 cycle and the phase 3 cyclewhich produce controllable pulses oi' current through the reactancewindings I2 through I5 will now be described. During phase 2 voltagealternations of one polarity, current ows through reactance winding i4and rectifiers 23 and 21, while opposite polarity alternations producecurrents in reactance winding I5 and rectiers 2! and 26. Similarly,dur-` ing phase 3 voltage alternations of one polarity, current flowsthrough reactance winding I2 and rectiers 22 and 21, while oppositepolarity alternations of phase 3 produce a current iiow throughreactance winding I3 and rectiers 24 and 26. During voltage alternationsof phase I the only available path in one direction is through bothreactance windings I2 and I5 as well as rectiiiers 22 and 25, while theonly available path for alternations of opposite polarity is throughreactance windings i3 and I4 and rectiflers 24I and 23. The greaterimpedance that results from the fact that an additional reactancewinding is included in these current paths of phase I, is normallysuiiicient to restrict the current ow during this phase to a very smallamount since the decreased flux produced by the reactance windings ineach circuit path will normally not produce saturation in the associatedreactors before the next current wave due to phase 2 or phase 3 isreceived by the reactance windings involved.

It will thus be seen that four controllable pulses of currentcorresponding to the rectified alternations ot phase 2 and phase 3 areprovided for every cycle of three phase power supply voltage. It hasbeen found that this circuit provides approximately 60% more outputvoltage than a comparable single phase circuit.

It will Ibe appreciated that rectiflers 26 and 21 are in circuitrelation with both effective phase cycles, namely phase 2 and phase 3,and thus eliminate the necessity for a separate pair of balancingrectifiers for the double bridge. Moreover, these rectiers 26 and 21alsoV function as commutating rectiiiers `for preventing any undesirablevoltage feedback if an inductive element is employed for load 28.

It is to be understood that many modications of the above-describedembodiment of my invention may be made. .Although l have shown, forexample, a single control winding in conjunction with each reactor coremember it and il, additional magnetic saturation controlling windings'for the purpose of varying the magnetic operating point or forconnection as a feedback winding, may also be employed. intend,therefore, by the appended claims to cover all such modiilcations asfall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent oi the UnitedStates is:

1. A three phase control system comprising, saturable reactor meanshaving two pair of reactance windings and at least one control windingfor controlling the level oi magnetic saturation of said reactor means,a direct current consumption circuit, three input conductors forconnection to a three phase alternating voltage source,4 and full-wavedouble-bridge current rectifying means connected in circuit relationwith each conductor and said consumption circuit to enable current to owthrough said consumption circuit in only one direction from two of saidconductors to a third conductor during each of four alternations ofsource voltage supplied between said latter two conductors and saidthird conductor during one three phase cycle of alternating voltagesupplied to said input conductors, and each pair of said reactancewindings being connected in circuit relation with each of said twoconductors and said consumption circuit to receive a respective one ofthe currents produced by said four alternations of source voltage.

2. A three phase control system comprising, saturable reactor meanshaving four reactance windings and a control winding for controlling thelevel of magnetic saturation in said reactor means, three inputterminals, a pair of output terminals, and full wave double-bridgecurrent rectifying means comprising six rectiilers, each of a ilrst pairof said rectiers being connected in reversed conductive relation with adifferent one of a first pair of said reactance windings to provide aseparate conduction path from diil'erent output terminals to the samerst one of said input terminals, each of a second pair of said rectiersbeing connected in reversed conductive relation with a diierent one of asecond pair of said reactance windings to provide a separate conductionpath from different output terminals to the same second one of saidinput terminals,

Kand a third pair of said rectiiiers each connected in reversedconductive relation from difterent output terminals to a third of saidinput termihals to effect a unidirectional current ow through a loadconnected across said output ,terminals during the four alternations ofa three phase source voltage supplied between said ilrst and third inputterminals and between said secondr and third input terminals,

RAYMOND E. MORGAN.

REFERENCES CITED The following references are of record in the le ofthis patent: f

UNITED STATES PATENTS Number Name Date 1,844,704 Thompson Feb. 9, 19321,955,322 Brown Apr. 17, 1934 2,552,952 Gachet et al May 15, 1951

